Orc sized? Really? He seems taller than all the other orcs to me. Like a good head or so.
As for the colour, why not? They are turning corrupted orc blood green, so why not ogres, too? I mean, they're using fel magic as well, no?
Ah, nevermind, there is a split second at the beginning of the scene where you can see his front. No second head. Never mind, then.
Edit: Sniped.
The mods of reddit/movies sure love taking down Warcraft promotional videos huh.
This looks like the portal before it was bound to an arcway that is the Dark Portal.
It seems they stepped out of the portal and fel magic hit Draka, who Gul'dan is kneeling down towards. She then births Go'el and he is green, which is the baby that Gul'dan holds up in the earlier trailers.
What... happened to the avatars...?